During launch, satellites are subjected to acceleration loads many times the acceleration due to gravity. This acceleration creates large loads on any spacecraft components not uniformly supported by the launch vehicle. To mitigate these loads and to better allow systems to fit within launch vehicle fairings, deployable structures are used to allow the compact packaging of otherwise large spacecraft components. For example, spacecraft solar arrays are often made deployable so that during launch they are well supported near the system bus. After launch, the array panels are deployed to lengths spanning many times the original bus dimensions. Additional applications of deployable structures in space are gravity gradient booms, instrument booms and various antennas for communications and radar missions.
The Storable Tubular Extendible Mast (STEM, Herzl, NASA SP-8065-1) is an example of a deployable structure. This structure uses a complex reel mechanism (canister) to store a highly stressed metal ribbon that once deployed, overlaps itself and forms a tube. Several variations of the STEM are commercially available from Northrop Grumman (Astro Aerospace). In a typical embodiment of STEM architectures, the tubes deploy from a canister that is fixed to the spacecraft. In U.S. Pat. No. 4,018,397, several tubes deploy from a single canister. The current invention improves upon these by configuring the booms in a new way such that the deployment control mechanism and canister are greatly simplified.